Re: [PATCH v2] arm64: perf: Add more support on caps under sysfs

Hi Will,

On 2021/6/3 0:42, Will Deacon wrote:

On Sat, May 29, 2021 at 02:19:46PM +0800, Shaokun Zhang wrote:

quoted

Armv8.7 has introduced BUS_SLOTS and BUS_WIDTH in PMMIR_EL1 register,
add two entries in caps for bus_slots and bus_width under sysfs. It
will return the true slots and width if the information is available,
otherwise it will return 0.

Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Shaokun Zhang <redacted>
---
ChangeLog:
v1-->v2:
    1. Address Robin's comment on bus_width calculation.
    2. Add the comment on calculation formula.

Will & Robin,

    I don't change any about visible, if have more comments,
please let me know.

 arch/arm64/include/asm/perf_event.h |  5 +++++
 arch/arm64/kernel/perf_event.c      | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
index 60731f602d3e..4ef6f19331f9 100644
--- a/arch/arm64/include/asm/perf_event.h
+++ b/arch/arm64/include/asm/perf_event.h

@@ -239,6 +239,11 @@
 /* PMMIR_EL1.SLOTS mask */
 #define ARMV8_PMU_SLOTS_MASK	0xff
 
+#define ARMV8_PMU_BUS_SLOTS_SHIFT 8
+#define ARMV8_PMU_BUS_SLOTS_MASK 0xff
+#define ARMV8_PMU_BUS_WIDTH_SHIFT 16
+#define ARMV8_PMU_BUS_WIDTH_MASK 0xf
+
 #ifdef CONFIG_PERF_EVENTS
 struct pt_regs;
 extern unsigned long perf_instruction_pointer(struct pt_regs *regs);

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index f594957e29bd..453e0d8a442e 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c

@@ -317,8 +317,43 @@ static ssize_t slots_show(struct device *dev, struct device_attribute *attr,
 
 static DEVICE_ATTR_RO(slots);
 
+static ssize_t bus_slots_show(struct device *dev, struct device_attribute *attr,
+			      char *page)
+{
+	struct pmu *pmu = dev_get_drvdata(dev);
+	struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
+	u32 bus_slots = (cpu_pmu->reg_pmmir >> ARMV8_PMU_BUS_SLOTS_SHIFT)
+			& ARMV8_PMU_BUS_SLOTS_MASK;
+
+	return snprintf(page, PAGE_SIZE, "0x%08x\n", bus_slots);

Can you use sysfs_emit() instead?

Ok,

quoted

+}
+
+static DEVICE_ATTR_RO(bus_slots);
+
+static ssize_t bus_width_show(struct device *dev, struct device_attribute *attr,
+			      char *page)
+{
+	struct pmu *pmu = dev_get_drvdata(dev);
+	struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
+	u32 bus_width = (cpu_pmu->reg_pmmir >> ARMV8_PMU_BUS_WIDTH_SHIFT)
+			& ARMV8_PMU_BUS_WIDTH_MASK;
+	u32 val;

Just initialise val to 0 here and drop the 'else' below.

Sure,

quoted

+	/* Encoded as Log2(number of bytes), plus one */
+	if (bus_width > 2 && bus_width < 13)
+		val = 1 << (bus_width - 1);
+	else
+		val = 0;
+
+	return snprintf(page, PAGE_SIZE, "0x%08x\n", val);

Again, sysfs_emit?

Got it and will fix these in next version.

Thanks,
Shaokun

Will
.

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